/* vi: set sw=4 ts=4: */
/*-------------------------------------------------------------------------
 * Filename:      xmodem.c
 * Copyright:     Copyright (C) 2001, Hewlett-Packard Company
 * Author:        Christopher Hoover <ch@hpl.hp.com>
 * Description:   xmodem functionality for uploading of kernels
 *                and the like
 * Created at:    Thu Dec 20 01:58:08 PST 2001
 *-----------------------------------------------------------------------*/
/*
 * xmodem.c: xmodem functionality for uploading of kernels and
 *            the like
 *
 * Copyright (C) 2001 Hewlett-Packard Laboratories
 *
 * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
 *
 * This was originally written for blob and then adapted for busybox.
 */

#include "libbb.h"

#define SOH 0x01
#define STX 0x02
#define EOT 0x04
#define ACK 0x06
#define NAK 0x15
#define BS  0x08

/*
Cf:
  http://www.textfiles.com/apple/xmodem
  http://www.phys.washington.edu/~belonis/xmodem/docxmodem.txt
  http://www.phys.washington.edu/~belonis/xmodem/docymodem.txt
  http://www.phys.washington.edu/~belonis/xmodem/modmprot.col
*/

#define TIMEOUT 1
#define TIMEOUT_LONG 10
#define MAXERRORS 10

#define read_fd  STDIN_FILENO
#define write_fd STDOUT_FILENO

static int read_byte(unsigned timeout)
{
	char buf[1];
	int n;

	alarm(timeout);
	/* NOT safe_read! We want ALRM to interrupt us */
	n = read(read_fd, buf, 1);
	alarm(0);
	if (n == 1)
		return (unsigned char)buf[0];
	return -1;
}

static int receive(/*int read_fd, */int file_fd)
{
	unsigned char blockBuf[1024];
	unsigned errors = 0;
	unsigned wantBlockNo = 1;
	unsigned length = 0;
	int do_crc = 1;
	char nak = 'C';
	unsigned timeout = TIMEOUT_LONG;

	/* Flush pending input */
	tcflush(read_fd, TCIFLUSH);

	/* Ask for CRC; if we get errors, we will go with checksum */
	full_write(write_fd, &nak, 1);

	for (;;) {
		int blockBegin;
		int blockNo, blockNoOnesCompl;
		int blockLength;
		int cksum_crc;	/* cksum OR crc */
		int expected;
		int i,j;

		blockBegin = read_byte(timeout);
		if (blockBegin < 0)
			goto timeout;

		timeout = TIMEOUT;
		nak = NAK;

		switch (blockBegin) {
		case SOH:
		case STX:
			break;

		case EOT:
			nak = ACK;
			full_write(write_fd, &nak, 1);
			return length;

		default:
			goto error;
		}

		/* block no */
		blockNo = read_byte(TIMEOUT);
		if (blockNo < 0)
			goto timeout;

		/* block no one's compliment */
		blockNoOnesCompl = read_byte(TIMEOUT);
		if (blockNoOnesCompl < 0)
			goto timeout;

		if (blockNo != (255 - blockNoOnesCompl)) {
			bb_error_msg("bad block ones compl");
			goto error;
		}

		blockLength = (blockBegin == SOH) ? 128 : 1024;

		for (i = 0; i < blockLength; i++) {
			int cc = read_byte(TIMEOUT);
			if (cc < 0)
				goto timeout;
			blockBuf[i] = cc;
		}

		if (do_crc) {
			cksum_crc = read_byte(TIMEOUT);
			if (cksum_crc < 0)
				goto timeout;
			cksum_crc = (cksum_crc << 8) | read_byte(TIMEOUT);
			if (cksum_crc < 0)
				goto timeout;
		} else {
			cksum_crc = read_byte(TIMEOUT);
			if (cksum_crc < 0)
				goto timeout;
		}

		if (blockNo == ((wantBlockNo - 1) & 0xff)) {
			/* a repeat of the last block is ok, just ignore it. */
			/* this also ignores the initial block 0 which is */
			/* meta data. */
			goto next;
		}
		if (blockNo != (wantBlockNo & 0xff)) {
			bb_error_msg("unexpected block no, 0x%08x, expecting 0x%08x", blockNo, wantBlockNo);
			goto error;
		}

		expected = 0;
		if (do_crc) {
			for (i = 0; i < blockLength; i++) {
				expected = expected ^ blockBuf[i] << 8;
				for (j = 0; j < 8; j++) {
					if (expected & 0x8000)
						expected = expected << 1 ^ 0x1021;
					else
						expected = expected << 1;
				}
			}
			expected &= 0xffff;
		} else {
			for (i = 0; i < blockLength; i++)
				expected += blockBuf[i];
			expected &= 0xff;
		}
		if (cksum_crc != expected) {
			bb_error_msg(do_crc ? "crc error, expected 0x%04x, got 0x%04x"
			                   : "checksum error, expected 0x%02x, got 0x%02x",
					    expected, cksum_crc);
			goto error;
		}

		wantBlockNo++;
		length += blockLength;

		errno = 0;
		if (full_write(file_fd, blockBuf, blockLength) != blockLength) {
			bb_perror_msg("can't write to file");
			goto fatal;
		}
 next:
		errors = 0;
		nak = ACK;
		full_write(write_fd, &nak, 1);
		continue;
 error:
 timeout:
		errors++;
		if (errors == MAXERRORS) {
			/* Abort */

			/* if were asking for crc, try again w/o crc */
			if (nak == 'C') {
				nak = NAK;
				errors = 0;
				do_crc = 0;
				goto timeout;
			}
			bb_error_msg("too many errors; giving up");
 fatal:
			/* 5 CAN followed by 5 BS. Don't try too hard... */
			safe_write(write_fd, "\030\030\030\030\030\010\010\010\010\010", 10);
			return -1;
		}

		/* Flush pending input */
		tcflush(read_fd, TCIFLUSH);

		full_write(write_fd, &nak, 1);
	} /* for (;;) */
}

static void sigalrm_handler(int ATTRIBUTE_UNUSED signum)
{
}

int rx_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int rx_main(int argc, char **argv)
{
	struct termios tty, orig_tty;
	int termios_err;
	int file_fd;
	int n;

	if (argc != 2)
		bb_show_usage();

	/* Disabled by vda:
	 * why we can't receive from stdin? Why we *require*
	 * controlling tty?? */
	/*read_fd = xopen(CURRENT_TTY, O_RDWR);*/
	file_fd = xopen(argv[1], O_RDWR|O_CREAT|O_TRUNC);

	termios_err = tcgetattr(read_fd, &tty);
	if (termios_err == 0) {
		orig_tty = tty;
		cfmakeraw(&tty);
		tcsetattr(read_fd, TCSAFLUSH, &tty);
	}

	/* No SA_RESTART: we want ALRM to interrupt read() */
	signal_no_SA_RESTART_empty_mask(SIGALRM, sigalrm_handler);

	n = receive(file_fd);

	if (termios_err == 0)
		tcsetattr(read_fd, TCSAFLUSH, &orig_tty);
	if (ENABLE_FEATURE_CLEAN_UP)
		close(file_fd);
	fflush_stdout_and_exit(n >= 0);
}
